Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes |
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| Authors: | Franziska DH Wilke Patrick J O'Brien Uwe Altenberger Matthias Konrad-Schmolke M Ahmed Khan |
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| Institution: | 1. Institut für Geowissenschaften, Universität Potsdam, D-14476 Potsdam, Germany;2. University of Sargodha, Sargodha, Pakistan;1. Department of Earth System Sciences, Yonsei University, Seoul 120-749, Republic of Korea;2. Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, Republic of Korea;3. Korea Basic Science Institute, Ochang, Cheongwon, Chungbuk 363-883, Republic of Korea;4. School of Earth Sciences and Resources, China University of Geosciences, Beijing, 29 Xueyuan Road, Beijing 100083, China;1. Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, USA;2. Laboratoire Géosciences Montpellier (CNRS-UMR 5243), Université Montpellier 2, 34095 Montpellier Cedex 5, France;3. School of Geosciences, University of Sydney, Sydney, NSW 2006, Australia;1. Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China;2. Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal;1. Department of Geology, University of Maryland, College Park, MD 20742, USA;2. Department of Geosciences, Boise State University, Boise, ID 83725, USA;3. Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, USA |
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| Abstract: | Metabasites were sampled from rock series of the subducted margin of the Indian Plate, the so-called Higher Himalayan Crystalline, in the Upper Kaghan Valley, Pakistan. These vary from corona dolerites, cropping out around Saif-ul-Muluk in the south, to coesite–eclogite close to the suture zone against rocks of the Kohistan arc in the north. Bulk rock major- and trace- element chemistry reveals essentially a single protolith as the source for five different eclogite types, which differ in fabric, modal mineralogy as well as in mineral chemistry. The study of newly-collected samples reveals coesite (confirmed by in situ Raman spectroscopy) in both garnet and omphacite. All eclogites show growth of amphiboles during exhumation. Within some coesite-bearing eclogites the presence of glaucophane cores to barroisite is noted whereas in most samples porphyroblastic sodic–calcic amphiboles are rimmed by more aluminous calcic amphibole (pargasite, tschermakite, and edenite). Eclogite facies rutile is replaced by ilmenite which itself is commonly surrounded by titanite. In addition, some eclogite bodies show leucocratic segregations containing phengite, quartz, zoisite and/or kyanite. The important implication is that the complex exhumation path shows stages of initial cooling during decompression (formation of glaucophane) followed by reheating: a very similar situation to that reported for the coesite-bearing eclogite series of the Tso Morari massif, India, 450 km to the south-east. |
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